The invention relates to a control system for a transmission comprising a torque converter or a hydrodynamic clutch in a motor vehicle for control or regulation of a starting operation of the motor vehicle.
Engines with exhaust gas turbo-charge are often used in modem motor vehicles having diesel prime movers. From ecological viewpoints an almost smoke-free operation of the diesel engine is sought in the whole range of operation. For the purpose can be injected only as much fuel as can be burnt without soot with the air mass delivered via the exhaust gas turbo-charger. When the engine is idling, the air mass delivered is accordingly small. The starting behavior of a motor vehicle thus motorized can be felt by the driver as unsatisfactory, especially in case of a quick and high power demand. The rise in rotational speed of the exhaust gas turbine and the increase associated therewith of the air mass charge directly limit the amount of fuel in the starting operation that can be injected for increasing the power in preventing a xe2x80x9csootingxe2x80x9d. Only with the rising rotational speed of the engine does the air mass charge increase and therewith the injection amount of fuel and consequently the engine torque. The torque increase at the beginning of the starting operation is accordingly low followed by a sharply progressive build up of the torque.
A similar problem results when using an otto engine turbo-charged with exhaust gas. The ecological critical value are here the exhaust gas composition in the idling operation and when greasing the fuel-air mixture during the starting operation. The air mass supplied to the engine by the turbo charge depends directly on the rotational speed of the exhaust gas turbine. The rotational speed acceleration of the exhaust gas turbine always occurs with a certain time offset relative to the power demand (accelerator pedal movement) of the driver more or less according to the size of the exhaust gas turbine. The driver feels this as an undesirably slow build up of the output torque of the vehicle usually designated as xe2x80x9cturbo-lagxe2x80x9d.
In relation to converter automatic transmissions, the starting weakness of a motor vehicle turbo-charged with exhaust gas can be positively affected via the characteristic of the torque converter (trilok converter). In the converter is usually provided a lock-up clutch by which the hydraulic power transmission can be mechanically bridged for reducing slip losses in the operation of the vehicle at high velocities. The hydrodynamic torque transmission produces a jerk-free starting operation with corresponding increased comfort. But it is disadvantageous for the starting dynamics that the engine rotational speed must accelerate in direction of the absorption torque of the torque converter. To this are also added as losses training torques of the drive train that necessarily exist. Since the absorption torque of a converter with strong torque reinforcement (xe2x80x9cweakxe2x80x9d converter characteristic) is smaller than the one in a converter with low torque reinforcement (xe2x80x9cstrongxe2x80x9d converter characteristic), the weakness described can be compensated, of course, at the cost of a xe2x80x9crubber-band likexe2x80x9d guiding behavior of the engine rotational speed due to the weak characteristic. The converter absorption torque generally increases sharply, especially in the cold, whereby the starting weakness is further worsened.
If a hydrodynamic clutch is used instead of a trilok converter, a similar problem arises. Due to the lack of stator opposite to the torque converter, the torque of the engine cannot be reinforced whereby another disadvantage results in the uninterrupted build up of the output torque of the motor vehicle. A hydrodynamic clutch also is often combined with a lock-up clutch in order to eliminate slip losses at high velocities of the vehicle.
U.S. Pat. No. 4,775,938 has disclosed a method for the control of a starting operation of a vehicle having a converter automatic transmission in which, during the starting operation of the vehicle the differential rotational speed of a starting clutch rear-mounted on the torque converter is regulated taking into account an accelerator pedal position of the engine as load standard in the calculation of the clutch pressure.
From U.S. Pat. No. 5,272,630 has become known a method of the control of a starting operation of a vehicle having a converter automatic transmission from a stationary uncoupling function, that is, of a starting operation with previously opened starting clutch. The converter slip is adjusted to a nominal differential rotational speed via the starting clutch to be re-engaged. A load standard of the driver acts as interference variable in the proposed control circuit.
Neither of the two methods results in any satisfactory performance in relation to the above described problem of the starting weakness of a driving train with diesel engine loaded with exhaust gas, since the acceleration behavior of the rotational speed and the actual power development of the prime mover remain without being taken into account (disregarded) in the clutch regulation and the closing operation of the starting dutch therefore acts as interference variable upon the rotational speed acceleration of the prime mover.
The invention is based on the problem of providing a control system which is improved the starting behavior of a transmission having a torque converter or a hydrodynamic clutch, the same as a torque-conducting and regulatable clutch or brake mounted in the transmission.
This problem is solved with a control system having the features stated in the main claim.
According to the invention, it is, therefore, proposed that the starting operation of the motor vehicle be regulated, as function of a driver""s wish, via a torque-conducting slip clutch or brake mounted in the transmission taking into account parameters of the torque converter or of the hydrodynamic clutch.
Via the slip in the torque-conducting clutch or brake, the rotational speed acceleration of the driving engine can be advantageously and purposefully controlled or adjusted. A turbo-lag described above, for example, is in this manner effectively prevented in the starting power of a vehicle with internal combustion engine loaded with exhaust gas.
The hydraulic absorption torque of the torque converter or of the hydraulic clutch to be applied by the engine becomes reduced to the extent to which the torque-conducting clutch or brake is opened, that is, brought to slip.
In the extreme case, the torque-conducting clutch or brake is briefly opened completely or almost completely up to the contact point, the piston, clutch or brake is in contact but transmission of torque has not occurred, that upon a power demand by the driver (accelerator pedal actuation) the engine can rotate at high speed almost free. Therefore, in the extreme case the engine acceleration is prevented in power flow direction until the open clutch or brake with the corresponding friction loss portions of the transmission, only by the rotatory inertia and the friction losses of the engine, the same as by the rotatory inertia of the rotary parts of the transmission, the loss portion of the converter absorption torque is completely eliminated.
Prior to and at the beginning of the starting operation the pressure in the torque-conducting clutch or brake is advantageously reduced to a value scarcely above the filling pressure of the clutch or brake, the piston of the clutch or brake thus remains at the contact point of the friction elements and a weak torque is transmitted. In this manner, the closing operation of the clutch or brake can be regulated shock-free and comfortably without dead times for the driver determined by the filling technology.
It has been found in tests that a small time offset between the power demand of the driver and the loose rolling of the vehicle, that is, the increase of the output rotational speed of the transmission, is not felt as negative, especially on account of the acoustic perception of the increasing rotational speed of the engine directly upon the accelerator pedal actuation. The slip regulation of the clutch or brake is conveniently carried out so that an optimum in starting power specific of the vehicle and mainly of the engine results.
A xe2x80x9crigidxe2x80x9d or also xe2x80x9chardxe2x80x9d characteristic of the torque converter or of the hydrodynamic clutch favorable to the dynamic operation can advantageously be provided with correspondingly direct guiding behavior of the engine rotational speed upon changes of the accelerator pedal by the driver in the prevalent operation in which a lock-up clutch of the converter is opened.
In a first inventive solution of the problem, it is proposed to regulate in the starting operation of the motor vehicle, as function of a driver""s wish, an output torque M_Ab of the transmission, especially a timed output torque curve M_Ab(t), via a torque conducting clutch or brake mounted in the transmission. Instead of the transmission output torque, a vehicle output torque obviously can also be used. An accelerator pedal movement of the driver is here advantageously interpreted directly as torque demand on the transmission output. The output torque M_Ab or the timed curve thereof M_Ab(t) is here primarily dependent on the curve of the clutch torque In the slip phase. At the moment of the slipping transmission clutch or transmission brake, the starting power of the motor vehicle is thus uncoupled from the actual torque build up of the prime mover, also from a torque reduction or also torque increase demanded in the course of the closing process of the clutch or brake by the transmission control during the engine control.
In one development of the invention it is proposed to regulate in the starting operation of the motor vehicle, as function of a driver""s wish, an output torque M_Ab of the transmission, especially a timed output torque curve M_Ab(t), via a torque conducting clutch or brake mounted in the transmission. Instead of the transmission output torque, a vehicle output torque obviously can also be used. An accelerator pedal movement of the driver is here advantageously interpreted directly as torque demand on the transmission output. The output torque M_Ab or the timed curve thereof M_Ab(t) is here primarily dependent on the curve of the clutch torque in the slip phase. At the moment of the slipping transmission clutch or transmission brake, the starting power of the motor vehicle is thus uncoupled from the actual torque build up of the prime mover, also from a torque reduction or also torque increase demanded in the course of the closing process of the clutch or brake by the transmission control during the engine control.
The regulation of the output torque M_Ab can thus be easuly attoned to a maximum possible starting power of the vehicle according to the actual power wish of the driver, for example, with linear torque build up on the transmission output.
A torque converter and a hydrodynamic clutch have a turbine which is torque-conductingly connected with the transmission input shaft. In a second inventive solution of the problem is proposed to regulate in the starting operation of the motor vehicle, as function of a driver""s wish, a torque M_T of said turbine, especially a timed turbine torque curve M_T(t), via a torque-conducting clutch or brake mounted in the transmission. Advantageously is hereby a power demand of the driver, on one hand, directly converted by control technology as torque standard, on the other handxe2x80x94in relation with type-dependent, structurally known parameters of the torque converter or of the hydrodynamic clutchxe2x80x94the engine rotational speed behavior subjectively important for the driver is also included in the regulation.
In another development of the invention is proposed to regulate in the starting operation of the vehicle, as function of a driver""s wish, a rotational speed n_T of the turbine of the torque converter or of the hydrodynamic clutch, especially a timed turbine rotational speed curve n_T(t), via a torque-conducting clutch or brake mounted in the transmission. Hereby it is advantageously possible, especially in relation to type-dependent, structurally known parameters of the torque converter or of the hydrodynamic clutch, easily to guide the engine rotational speed n_Mot so that there always result for the driver during the starting operation a clearly understandable correlation between his pedal movement and the consequent behavior of the engine.
In a development for regulating the turbine rotational speed n_T, it can be provided to use as regulation variable the gradient dn_T/dt thereof. The advantage attained hereby in the regulation dynamics, by preventing perceptible over oscillations of the of the engine rotational speed as consequence of a too belated reaction on the pressure side in the torque-conducting clutch or brake, especially in case of a quick and high power demand, acts positively both in starting comfort and in the safety relative to dutch damages.
In a further development of the regulation of the turbine rotational speed n_T, of the timed curve n_T(t) of the turbine rotational speed, or of the turbine rotational speed gradient dn_T/dt, it can be provided that the respective regulation variables n_T, n_T(t) and dn_T/dt be function of the distance to the synchronization point of the closing operation of the torque-conducting clutch or brake. Hereby can be further improved the closing comfort of the clutch or brake, especially in the range of low slip rotational speeds.
Torque converter and hydrodynamic clutch have, together with the turbine, a pump which is connected with the driving engine in torque-conducting manner. The power is hydrodynamically transmitted from the pump to the turbine. In another development of the invention is proposed, in the starting operation of the motor vehicle, to regulate, as function of a driver""s wish, a rotational speed ratio nue, which is defined as quotient of turbine rotational speed n_T and pump rotational speed n_P of the torque converter or of the hydrodynamic dutch, via a torque-conducting clutch or brake mounted in the transmission, especially taking into account the converter type used (torque converter or hydrodynamic clutch) and/or a temperature.
As parameters of the converter type are specially to be regarded the known structural rating values maximum converter reinforcement mue_max, converter pump torque M_P2000 (at an input rotational speed of 2000 1/min), but also the known converter diagrams with the functions pump torque MT_T=f(pump rotational speed n_P), torque behavior mue=f(rotational speed ratio nue) with mue=turbine torque M_T/pump torque M_P and nue=n_T/n_P, converter efficiency degree=f(rotational speed ratio nue), turbine torque M_T=f(turbine rotational speed n_T), pump rotational speed n_P=f(turbine rotational speed n_T), converter efficiency degree=f(turbine rotational speed n_T).
As temperature to be taken into account in the regulation, the transmission oil temperature is particularly to be provided, since it affects to a substantial extent the efficiency degree of the hydrodynamic circuit in the torque converter or in the hydrodynamic clutch and therewith the absorption torque. As substitute variables for the transmission oil temperature can also be used an engine oil temperature, a cold water temperature, or also an outer air temperature. Instead of a sensed temperature can also be used an imaginary temperature calculated via a suitable temperature pattern.
It thus advantageously results from the point of view of control technology a simple relation to the type-dependent, structurally known parameters of the torque converter or of the hydrodynamic clutch. Specially by taking into account the transmission oil temperature (or a corresponding substitute temperature) it is definitely possible to improve the starting power of a vehicle with exhaust gas turbo-charged internal combustion engine at low temperatures when, for example, the slip time of the torque-conducting clutch or brake is extended toward low temperatures or when the time portion is increased toward low temperatures with large clutch slip immediately at the beginning of the starting operation.
In a third inventive solution of the problem is proposed to regulate in the starting operation of the vehicle, as function of a driver""s wish, a rotational speed ratio mue defined as quotient of turbine torque M_T and pump torque M_P of the torque converter or of the hydrodynamic clutch via a torque-conducting clutch or brake mounted in the transmission, especially taking into account the converter type (torque converter or hydrodynamic clutch) and/or a temperature. In this development is advantageous, on one hand, the easy adjustability according to control technology to converter typical influences on the starting power of the motor vehicle, on the other hand, also the torque orientation of the regulation already described above. As parameters of the torque converter or of the hydrodynamic clutch can be preferably be used parameters described above in relation to the regulation of the rotational speed ratio nue. The temperature can preferably be determinedxe2x80x94as also described alreadyxe2x80x94from a transmission oil temperature and/or engine oil temperature and/or engine coolant temperature and/or air temperature and/or calculated imaginary temperature.
In other embodiments of the invention is proposed, in the starting operation to regulate, as function of a driver""s wish, an acceleration a_Fzg or a velocity v_Fzg of the motor vehicle, particularly the timed curve a_Fzg(t) or v_Fzg(t) thereof, via a torque-conducting clutch or brake mounted in the transmission. Of special advantage is here the good correlation according to automatic regulation technology to subjective perception of the driver who always feels his demand performance as vehicle acceleration and velocity increment.
In other developments of the invention is proposed, in the starting operation to regulate, as function of a driver""s wish, an acceleration a_Fzg or a velocity v_Fzg of the motor vehicle, particularly the timed curve a_Fzg(t) or v_Fzg(t) thereof, via a torque-conducting clutch or brake mounted in the transmission. Of special advantage is here the good correlation according to automatic regulation technology to subjective perception of the driver who always feels his demand performance as vehicle acceleration and velocity increment.